In the January issue of Flying magazine, there's a neat article about the Air National Guard (ANG) in Ohio. The writer explains his experience when flying in a KC-135R Stratotanker with the 121st Air Refueling Wing of the ANG of Ohio while on a mid-air refueling training mission over the eastern USA.

During the pre-flight inspections, it was noted that their KC-135R had 2 squawks/snags in the maintenance logs. The first squawk was in reference to the ADF, and the second was about vortex generators.

From the article ...............

"One vortex generator was missing from the bottom of the left horizontal stabilizer. It's okay to fly with two gone, and this was deferred to the next major maintenance."

My interpretation of the above sentence is that vortex generators (VG's) are on the KC-135's MEL list, and that the limit of missing VG's that can be deferred is only 2. If more than 2 VG's are noticed missing during a walk-around inspection, the aircraft will be grounded untill they're replaced. Have I understood this correctly?

So, my questions are .................

Do commercial airliners that use vortex generators on their wings, tails, flaps, etc, also have a set limit of VG's that can be missing in the airliner's MEL list? If the answer is yes, can someone give examples?

it would be interesting to learn that the need for such small objects could ground an airliner.

NOTES:
1. There is no performance penalty.
2. During cruise flight, occasional vertical
motions may be felt which appear to be light
turbu lence. These mot ions are
characteristic of this airplane and should not
be construed as associated with Mach
buffet.

>>>The small yellow object just forward of Spoiler # 4 is not a vortex generator or vortilon. What is it?

While it looks like just another vortex generator, this one has another function. In the event of an evacuation using the over-wing emergency exits, there's a little length of rope/cord stored that one deploys and clips to this yellow fitting. There's also one on the opposite side of the aircraft. IIRC, you'll only see them on 737-100s and 737-200s, since Boeing discontinued them on the 737-300s and later variants.

Can someone give a quick explanation of what these do exactly? As in, why is it necessary to generate vortices on the upper wing and h stab surface? Thanks...
~Vik

I don't know what they accomplish on airliners, but on light aircraft, they disturb the boundry layer airflow and delay seperation at high angels of attack when installed on the wing. This lets you fly at a higher AoA (and lower airspeed) without stalling.

In twins, I believe it has something to do with increasing rudder authority and reducing Vmc, but as I don't have a "MEL" printed on my certificate yet, I really couldn't say .

> Vikkyvik, vortex generators create a vortex which helps the airflow over a wing stay atached to the wing during high angles of atack & slow airspeeds. It helps prevent a laminar airflow's boundary layer from separating from a wings surface, thus preventing a stalling condition.

Well, your answer sure makes a lot more sense than mine! I wasn't serious about my answer though, I was just saying what it looked like it was for. I know that mechanics have large tripod type stands that hook into the lower sides of an airliner's fuselage for the purpose of lifting it off the ground.

You mentioned .............

you'll only see them on 737-100s and 737-200s, since Boeing discontinued them on the 737-300s and later variants

Well, not to be nic-picking but, the 737 in the Pop Quiz photo is a -376 model. So I guess Boeing waited ontill the -400 series to stop using those yellow hook-ups.

While it looks like just another vortex generator, this one has another function. In the event of an evacuation using the over-wing emergency exits, there's a little length of rope/cord stored that one deploys and clips to this yellow fitting.

OPNLguy has it right!

It appears to be an atachment point where a cable or hook might be used to lift the whole airliner up off a hangar floor .......... pretty far fetched eh?

None of our -300s (that I know of) have them, and I just assumed that Boeing stopped installing them, since we (SWA) were a launch customer (along with USAir) on the -300. Guess they still offer them as an option...

For interest's sake the retrofit VG kit available for Piper Navajo/Chieftains allows a higher MTOW. This is because the one engine inoperative (OEI) rate of climb required in this category is related to the stall speed, which is lower with the addition of VGs -> can carry more weight.

Can someone give a quick explanation of what these do exactly? As in, why is it necessary to generate vortices on the upper wing and h stab surface? Thanks...

In general, they turbulate the airflow over the wing, thus added total KE to the flow and allowing it to travel further along the wing before seperating, much like dimples on a golf ball do. This is obviously useful at close-to-stall speeds/high AoA.

I'm not sure, but I don't think that their typical usage would differ greatly between lights, twins, and airliners, however there might be some differences.